Over the past several years, a great deal of research has been directed to the design of biodegradable polymers. Concern over waste disposal, particularly of packaging materials, disposable diapers, etc., motivates much of this work. Products designed to degrade after their intended use may be composed of photosensitive or hydrolytically degradable polymers. Polymers intended to degrade during use, as in controlled-release delivery systems, are nearly always hydrolytically degradable. Hydrolytically degradable polymers are frequently polyester-based, prepared by condensation or radical polymerization. Also employed are physically or chemically bonded blends of synthetic polymers with biomaterials such as starch.
For many purposes, the superior physical properties provided by polyolefins prepared by addition polymerization are desirable. To date, however, incorporation of polar groups into such polyolefins has had limited success, since many polar monomers poison, or competitively coordinate with, the organometallic polymerization catalysts that are typically used. Copolymers of olefins, such as ethylene, with polar monomers such as acrylates, were initially limited to block copolymers, formed by two-stage polymerization, e.g., by post-polymerization of an acrylate or methacylrate monomer onto a previously formed polyolefin chain (Yasuda et al., 1996, 1997; Goto et al, Hajime et al.). Masakazu et al., in JP Kokai 4-45108 (1992), described the preparation of an ethylene copolymer containing 4.7 mole % ethyl acrylate, Mn 9,100, Mw 22,500, that show improved adhesion over polyethylene homopolymer. Johnson et al. (1996) described the formation of random olefin-acrylate copolymers using Brookhart-type catalysts. None of these polymers, however, include a hydrolyzable linkage in the backbone of the polymer, and therefore they would not be hydrolytically degradable. Ouchi et al. described free radical copolymerization of diallylidene pentaerythritol with styrene; however, incorporation of the diene monomer was low, and increased incorporation significantly decreased the intrinsic viscosity of the product. The reaction conditions would also be expected to produce a non-stereoregular polymer.
Accordingly, providing olefin copolymers that have good physical properties and stability under conditions of use, at neutral or near-neutral pH, but that degrade into soluble or easily dispersable particles in an aqueous medium would be desirable.